This invention relates generally to contoured transparencies such as aircraft windshields and canopies, and, more particularly, to transparencies configured to reduce optical distortion.
Windshields and canopies of modern aircraft are frequently highly contoured, having large amounts of curvature, and the pilots must look through the transparencies at highly oblique angles. These transparency configurations can bring about significant optical distortion and sighting errors. For example, angular deviation of the pilots line of sight can cause objects to be observed in the sky at apparent locations displaced significantly from their actual locations. This is an extremely critical drawback, especially when the objects being sighted are other aircraft.
In addition, the transparency configurations can alter the lines of sight of the pilot's two eyes by different amounts, such that each eye perceives the object to be in a different location. This phenonemon, called binocular deviation, can cause severe eye fatigue and headaches, and in extreme cases can cause image separation, or double vision.
In the past, it has been commonly believed that optical distortion and sighting errors could be minimized by forming the transparencies with precisely uniform thickness over their entire areas. Thus, great care has been taken in manufacturing the tooling and in refining the grinding and polishing techniques used in producing these transparent sheets. Despite this care, transparencies having a uniform thickness still provide significant distortion and sighting errors.
The designers of some aircraft systems, such as Heads-Up Display (HUD) systems, have sought to compensate for some sighting errors introduced by such transparencies by providing corrections based on optical deviation test results. This is believed to unduly complicate the HUD system and thereby to add significantly to its cost.
It should be appreciated from the foregoing that there is a definite need for an improved contoured transparency that provides reduced distortion of light passing through it at an oblique angle. In particular, there is a need for a transparency such as an aircraft windshield or canopy that substantially eliminates optical distortion such as angular deviation, or, alternatively, binocular deviation. The present invention fulfills this need.